Mattress overlay



FIG. 1 is a top plan view of a mattress overlay showing the top surface of our new design;

FIG. 2 is a right side elevational view of our design, with the left side elevational view being identical thereto;

FIG. 3 is a front elevational view of the mattress overlay, with the rear elevational view being identical thereto; and

FIG. 4 is a bottom plan view of the mattress overlay. 

The ornamental design for a mattress overlay, as shown and described. 